Slow magnetic relaxation in Nd(iii) and Sm(iii) complexes formed in three-dimensional lanthanide-dicyanidometallate(i) frameworks exhibiting luminescent properties

Abstract

Coordination network-based magnets composed of uncommon Kramers ions (Nd(III) and Sm(III)) exhibit emissive properties and may realize diverse magneto-optical applications. Herein we characterize cyanide-bridged robust networks possessing lanthanide ions combined with dicyanidometallates(I) crystallizing in three-dimensional (3D) [Ln^III(H₂O)₃][M^I(CN)₂]₃ (Ln^III = Nd, Sm; M^I = Ag, Au; NdAg, NdAu, SmAg, and SmAu) coordination polymers. Each Ln^III centre is coordinated by six cyanido ligands and three water molecules, resulting in a tricapped trigonal prism coordination geometry and single-molecule magnet (SMM) properties. Alternating current magnetic studies confirm the presence of a slow magnetic relaxation with calculated energy barriers of 18.8, 25.6, 26.9, and 22.3 K for NdAg, NdAu, SmAg, and SmAu, respectively. To understand the magnetic anisotropy of the central Ln(III) ions and the effect on the Kramers doublet splitting, ab initio calculations are conducted and a suitable magnetic anisotropy for Sm(III)-SMMs is explored to enhance the energy barrier. The Nd(III) and Sm(III) ions are characterized by weakly anisotropic magnetic properties and an easy-plane magnetic character, respectively. Additionally, the compounds show visible emissions. The Nd(III)-containing frameworks exhibit bluish emissions from the [Ag(CN)₂]_n/[Au(CN)₂]_n centres. SmAg and SmAu display multi-coloured emissions upon cooling with the photoluminescence colours ranging from magenta to blue, depending on the temperature. Due to the sharp increase in the emission intensity for SmAu, its thermal sensing ability is also investigated. The maximum relative thermal sensitivity of 3.50% K⁻¹ (at 80 K) for SmAu is the highest among Sm(III)-containing SMMs in a 3D framework.